Method and system for multiple channel wireless transmitter and receiver phase and amplitude calibration

ABSTRACT

The present invention provides a method and system for estimating common amplitude and phase errors of a multiple channel wireless system. The multiple channel wireless system includes a plurality of transmission channels formed between a plurality of transmission antennas and a plurality of receiver antennas. The method includes estimating transmission channel elements between each transmission antenna and receiver antenna pair of the multiple channel wireless system. Calibration symbols are transmitted from each transmit antenna. Signals are received that correspond to the calibration symbols having traveled through the transmission channels. Received calibration symbols are estimated based upon spatial processing of the received signals and the estimated transmission channel elements. Common amplitude and phase errors are estimated for each transmit and receive antenna pair by comparing the transmitted calibration symbols with the received calibration symbols.

FIELD OF THE INVENTION

The invention relates generally to a wireless communications receiverhaving multiple receiver channels wireless communications. Moreparticularly, the invention relates to a method and system forcalibrating phase and amplitude errors associated with the multiplechannel transmitters and receivers.

BACKGROUND OF THE INVENTION

Wireless communication systems commonly include information-carryingmodulated carrier signals that are wirelessly transmitted from atransmission source (for example, a base transceiver station) to one ormore receivers (for example, subscriber units) within an area or region.

A form of wireless communication includes multiple transmit antennaeand/or multiple receiver antennae. Multiple antennae communicationsystems can support communication diversity and spatial multiplexing.

A Wireless Channel

FIG. 1 shows modulated carrier signals traveling from a transmitter 110to a receiver 120 following many different (multiple) transmissionpaths.

Multipath can include a composition of a primary signal plus duplicateor echoed images caused by reflections of signals off objects betweenthe transmitter and receiver. The receiver may receive the primarysignal sent by the transmitter, but also receives secondary signals thatare reflected off objects located in the signal path. The reflectedsignals arrive at the receiver later than the primary signal. Due tothis misalignment, the multipath signals can cause intersymbolinterference or distortion of the received signal.

The actual received signal can include a combination of a primary andseveral reflected signals. Because the distance traveled by the originalsignal is shorter than the reflected signals, the signals are receivedat different times. The time difference between the first received andthe last received signal is called the delay spread and can be as greatas several micro-seconds.

The multiple paths traveled by the modulated carrier signal typicallyresults in fading of the modulated carrier signal. Fading causes themodulated carrier signal to attenuate in amplitude when multiple pathssubtractively combine.

Spatial multiplexing and diversity communication are transmissiontechnologies that exploit multiple antennae at both the base transceiverstation and at the subscriber units to increase the bit rate in awireless radio link with no additional power or bandwidth consumption.

FIG. 2 shows three transmitter antenna arrays 210, 220, 230 thattransmit data symbols to a receiver antenna array 240. Each transmitterantenna array and each receiver antenna array include spatially separateantennae. A receiver connected to the receiver antenna array 240separates the received signals.

Common Amplitude and Phase Errors

Multiple channel transmitters and receivers are generally associatedwith spatial multiplexing or diversity signals. Multiple channeltransmitters and multiple channel receivers can include multipletransmitter and receiver chains.

The multiple transmitter and receiver chains typically include amplitudenoise and phase noise that vary over time. Generally, the rate in whichthe amplitude noise and phase noise vary is greater than a rate in whichthe transmission channel between the transmitter and receiver varies.

Channel training can be used to characterize the amplitude and phasenoise. Channel training, however, requires a large amount of electronicsoverhead, and requires the transmission of a large amount of calibrationinformation. Additionally, training is not very effective incharacterizing amplitude and phase noise if the amplitude and phasenoise is changing quickly.

Prior art multiple channel transmitters and multiple channel receivergenerally each include a common clock that is associated withtransmitter channels or the receiver channels. That is, prior artmultiple chain transmitters generally include a common clock forenabling transmission from each of the multiple transmitter chains.Prior art multiple chain receivers generally include a common clock forenabling reception from each of the multiple receiver chains. Therefore,phase and amplitude errors associated with multiple chain transmittersand multiple chain receivers are generally ignored.

More advanced multiple channel wireless systems can include thetransmitter chains being individually clocked, and the receiver chainsbeing individually clocked. For example, some advanced systems includeeach transmitter residing at a separate base transmitter station(multiple base multiple channel system).

Multiple base spatial multiplexing or transmitter diversity systems canbe much more sensitive to phase and amplitude errors than single basesystems. Calibration of the phase and amplitude errors can be much moredifficult because each transmitter chain is synchronized to a differentclock. Multiple chain receivers having different clocks associated witheach receiver chain are also difficult to calibrate.

Some wireless systems (such as mobile wireless systems and local areanetworks (LANs)) include interfacing transmitters and receivers that aremanufactured by different companies. This can result in receivers andtransmitters that include varying types of transmission and receiverchains that each influence amplitude and phase noise differently. Inaddition, these systems can include transmission from mobiletransmitters having varied transmission channels.

It is desirable to have a method and system for calibrating phase andamplitude errors associated with transmitting and receiving multipleinformation signals with transmission and receiver chains thatindividually contribute phase and amplitude noise. The method and systemshould be adaptable for use with presently existing multiple channelsystems without adding appreciable cost. The method and system shouldallow for the transmission of higher orders of modulation.

SUMMARY OF THE INVENTION

The invention includes a method and system for calibrating phase andamplitude errors associated with transmitting and receiving multipleinformation signals between transmission and receiver chains that areindividually clocked, spatially separate or include varying types ofelectronic components. The method and system can be adapted for use withpresently existing multiple channel systems without adding appreciablecost. The method and system allows for the transmission of higher ordersof modulation.

A first embodiment of the invention includes a method for estimatingcommon amplitude and phase errors of a multiple channel wireless system.The multiple channel wireless system includes a plurality oftransmission channels formed between a plurality of transmissionantennas and a plurality of receiver antennas. The method includesestimating transmission channel elements between each transmissionantenna and receiver antenna pair of the multiple channel wirelesssystem. Calibration symbols are transmitted from each transmit antenna.Signals are received that correspond to the calibration symbols havingtraveled through the transmission channels. Received calibration symbolsare estimated based upon spatial processing of the received signals andthe estimated transmission channel elements. Common amplitude and phaseerrors are estimated for each transmit and receive antenna pair bycomparing the transmitted calibration symbols with the receivedcalibration symbols.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art wireless system that includes multiple pathsfrom a system transmitter to a system receiver.

FIG. 2 shows a prior art wireless system that includes spatiallyseparate transmitter antennae and spatially separate receiver antennae.

FIG. 3 shows an embodiment of the invention.

FIG. 4 show constellations of symbols that have been transmitted byseparately clocked transmitter antennas.

FIG. 5 shows another embodiment of the invention.

FIG. 6 shows another embodiment of the invention.

FIG. 7 shows another embodiment of the invention.

FIG. 8 shows another embodiment of the invention.

FIG. 9 shows a flow chart of steps or acts included within an embodimentof the invention.

FIG. 10 shows a flow chart of steps or acts included within anotherembodiment of the invention.

FIG. 11 shows a flow chart of steps or acts included within anotherembodiment of the invention.

FIG. 12 shows a flow chart of steps or acts included within anotherembodiment of the invention.

DETAILED DESCRIPTION

As shown in the drawings for purposes of illustration, the invention isembodied in a method and system for calibrating phase and amplitudeerrors associated with transmitting and receiving multiple informationsignals between transmission and receiver chains that are individuallyclocked, spatially separate or include varying types of electroniccomponents. The method and system can be adapted for use with presentlyexisting multiple channel systems without adding appreciable cost. Themethod and system allows for the transmission of higher orders ofmodulation.

Particular embodiments of the present invention will now be described indetail with reference to the drawing figures. The techniques of thepresent invention may be implemented in various different types ofwireless communication systems. Of particular relevance are cellularwireless communication systems. A base station transmits downlinksignals over wireless channels to multiple subscribers. In addition, thesubscribers transmit uplink signals over the wireless channels to thebase station. Thus, for downlink communication the base station is atransmitter and the subscribers are receivers, while for uplinkcommunication the base station is a receiver and the subscribers aretransmitters. Subscribers may be mobile or fixed. Exemplary subscribersinclude devices such as portable telephones, car phones, and stationaryreceivers such as a wireless modem at a fixed location.

The base station can be provided with multiple antennas that allowantenna diversity techniques and/or spatial multiplexing techniques. Inaddition, each subscriber can be equipped with multiple antennas thatpermit further spatial multiplexing and/or antenna diversity. SingleInput Multiple Output (SIMO), Multiple Input Single Output (MISO) orMultiple Input Multiple Output (MIMO) configurations are all possible.In either of these configurations, the communications techniques canemploy single-carrier or multi-carrier communications techniques.Although the techniques of the present invention apply topoint-to-multipoint systems, they are not limited to such systems, butapply to any wireless communication system having at least two devicesin wireless communication. Accordingly, for simplicity, the followingdescription will focus on the invention as applied to a singletransmitter-receiver pair, even though it is understood that it appliesto systems with any number of such pairs.

Point-to-multipoint applications of the invention can include varioustypes of multiple access schemes. Such schemes include, but are notlimited to, time division multiple access (TDMA), frequency divisionmultiple access (FDMA), code division multiple access (CDMA), orthogonalfrequency division multiple access (OFDMA) and wavelet division multipleaccess.

The transmission can be time division duplex (TDD). That is, thedownlink transmission can occupy the same channel (same transmissionfrequency) as the uplink transmission, but occur at different times.Alternatively, the transmission can be frequency division duplex (FDD).That is, the downlink transmission can be at a different frequency thanthe uplink transmission. FDD allows downlink transmission and uplinktransmission to occur simultaneously.

Typically, variations of the wireless channels cause uplink and downlinksignals to experience fluctuating levels of attenuation, interference,multi-path fading and other deleterious effects. In addition, thepresence of multiple signal paths (due to reflections off buildings andother obstacles in the propagation environment) causes variations ofchannel response over the frequency bandwidth, and these variations maychange with time as well. As a result, there are temporal changes inchannel communication parameters such as data capacity, spectralefficiency, throughput, and signal quality parameters, e.g.,signal-to-interference and noise ratio (SINR), and signal-to-noise ratio(SNR).

Information is transmitted over the wireless channel using one ofvarious possible transmission modes. For the purposes of the presentapplication, a transmission mode is defined to be a particularmodulation type and rate, a particular code type and rate, and may alsoinclude other controlled aspects of transmission such as the use ofantenna diversity or spatial multiplexing. Using a particulartransmission mode, data intended for communication over the wirelesschannel is coded, modulated, and transmitted. Examples of typical codingmodes are convolution and block codes, and more particularly, codesknown in the art such as Hamming Codes, Cyclic Codes and Reed-SolomonCodes. Examples of typical modulation modes are circular constellationssuch as BPSK, QPSK, and other m-ary PSK, square constellations such as4QAM, 16QAM, and other m-ary QAM. Additional popular modulationtechniques include GMSK and m-ary FSK. The implementation and use ofthese various transmission modes in communication systems is well knownin the art.

For channels with significant delay-spread, typically orthogonalfrequency division multiplexing (OFDM) modulation system (as will bedescribed later) is employed. In an OFDM system that includes multiplefrequency tones, the delay spread results in each frequency tone havinga different fade.

FIG. 3 shows an embodiment of the invention. This embodiment includesmultiple transmitters including a plurality of transmitter antennas T1,T2, and a plurality of receiver antennas R1, R2. This embodiment onlyincludes two transmitter antennas and two receiver antennas. However, itis to be understood that the invention can include embodiments thatinclude either multiple transmit antennas, or multiple receiverantennas.

A first transmit chain 310 receives symbols (S1) for transmission from afirst transmit antenna T1. A second transmit chain 320 receives symbols(S2) for transmission from a second transmit antenna T2. The firsttransmit chain 310 and the second transmit chain 320 can be spatiallyseparate. The first transmit chain 310 can include a frequencyup-conversion block 312. The second transmit chain 320 can include afrequency up-conversion block 322. The first transmit chain 310 and thesecond transmit chain 320 can be synchronized to separate clocks.

A multiple chain receiver can include a first receiver antenna R1 and asecond receiver antenna R2. The first receiver antenna R1 can beassociated with a first receiver chain that typically includes afrequency down-conversion unit 330. The second receiver antenna R2 canbe associated with a second receiver chain that typically includes afrequency down-conversion unit 340. The first receiver chain and thesecond receiver chain can be synchronized to separate frequencyreferences (clocks).

The transmission channels between the transmitter antennas T1, T2 andthe receiver antennas R1, R2 are generally characterized by a channelmatrix H. A first vector representing the channels between the firsttransmitter antenna T1 and the first receiver antenna R1 and the secondreceiver antenna R2 is designated as h1 in FIG. 3. A second vectorrepresenting the channels between the second transmitter antenna T2 andthe first receiver antenna R1 and the second receiver antenna R2 isdesignated as h2 in FIG. 3. The channel matrix H includes the firstvector h1 and the second vector h2.

The receiver includes a spatial processing and decode unit 350. Thespatial processing and decode unit 350 generates estimates of theoriginally transmitted symbols base upon the channel matrix H andsymbols that are received.

The received information signals can be transmitted from a transmitterthat includes k spatial separate streams. Generally, such a transmitterapplies an encoding mode to each of the k streams to encode the data tobe transmitted. Before transmission, the data may be interleaved andpre-coded. Interleaving and pre-coding are well known in the art ofcommunication systems. The transmission rate or throughput of the datavaries depending upon the modulation, coding rates and transmissionscheme (diversity or spatial multiplexing) used in each of the kstreams.

The spatial processing and decode unit 350 performs receive processingto recover the k encoded streams. The recovered k streams are signaldetected, decoded and de-multiplexed for recovery the data. In the caseof antenna diversity processing, it should be understood that k is equalto one and thus there is only a single stream recovered.

An embodiment of the invention includes first estimating transmissionchannel elements between each transmission antenna and receiver antennapair of the multiple channel wireless system. Next, calibration symbolsare transmitted from each transmit antenna. Signals are received thatcorrespond to the calibration symbols having traveled through thetransmission channels. Received calibration symbols are estimated basedupon spatial processing of the received signals and the estimatedtransmission channel elements common amplitude and phase errors for eachtransmit and receive antenna pair are estimated by comparing thetransmitted calibration symbols with the received calibration symbols.

FIG. 4 show constellations of symbols that have been transmitted byseparately clocked transmitter antennas. A first transmitter antenna T1transmits a first constellation 410, and a second transmitter antenna T2transmits a second constellation 420. A received constellation 430 showshow phase and amplitude errors in different transmit and receive chainscan distort a received constellation of the transmitted constellations.The constellations can be rotated (due to phase distortion), and shiftedaway from or towards the origin (due to amplitude distortion).

FIG. 5 shows another embodiment of the invention. This embodimentincludes multiple transmit antennas T1, T2 . . . TM. Each transmitantenna transmits a corresponding calibration symbol c1, c2 . . . cM.The transmitted calibration symbols symbol c1, c2 . . . cM travelthrough a transmission channel represented by a channel matrix H, andare received by receiver antennas R1, R2 . . . RN.

A spatial processor 510 generates estimates of the originallytransmitted calibration symbol c1, c2 . . . cM using receivedcalibration symbols x1, x2 . . . xN, and the channel matrix H.

A compare block 520 compares the estimates with the actually transmittedcalibration symbol c1, c2 . . . cM to generate error factors e1, e2 . .. eM to be used for correcting the phase and amplitude errors of datasymbols subsequently transmitted.

Generally, x=Hc+n, where x is a vector representing the received signalsx1, x2 . . . xN, H is the channel matrix, c is a vector representing thetransmitted calibration symbols c1, c2 . . . cM, and n representsadditive noise.

An embodiment of the spatial processor 510 includes a maximum likelihood(ML) receiver. An estimate c of the transmitted calibration symbols canbe given as;c=argmin _(ct) ∥x−Hct∥ _(F),where ∥.∥ is the Frobenius norm, and ct represents all of the possibleconstellations of c.

Another embodiment of the spatial processor 510 includes a minimum meansquare error (MMSE) receiver. An estimate c of the transmittedcalibration symbols can be given as;c=H*(HH*+R _(nn))⁻¹ x, where R_(nn) is the noise covariance matrixestimated at the receiver.

Another embodiment of the spatial processor 510 includes a zero forcing(ZF) receiver. An estimate c of the transmitted calibration symbols canbe given as;c=H*(HH*)⁻¹ x

The common phase and amplitude errors are then calculated within thecompare block 520. The common phase and amplitude error between the jthtransmitter and the receiver is calculated by comparing the transmittedcalibration symbols c_(j) and the received estimate of the transmittedcalibration symbols c_(j) as follows:e _(j)=(c _(j))/(c _(j))

The calculated common phase and amplitude errors can be used to correctestimated data symbols that are transmitted from the transmit antennasT1, T2 . . . TM, and received by the receiver antennas R1, R2 . . . RN.

FIG. 6 shows another embodiment of the invention. This embodiment isgenerally applicable to multiple transmitter antenna, multiple receiverantenna systems in which the multiple receiver chains are independent.Generally, independent receiver chains are synchronized to independentreference oscillators, have different RF components, or each receiverchain is geographical located in a different place.

This embodiment includes multiple transmit antennas T1, T2 . . . TM.Each transmit antenna transmits a corresponding calibration symbol c1,c2 . . . cM. The transmitted calibration symbols symbol c1, c2 . . . cMtravel through a transmission channel represented by a channel matrix H,and are received by receiver antennas R1, R2 . . . RN.

The H matrix includes M by N elements, in which each element can benumbered as indicated in FIG. 6.

A common phase and amplitude error e_(j) between an ith receiver antennaand the transmitter can be calculated by transmitting a known, identicaltransmission calibration symbols c=c1=c2=cM from all of the T1, T2 . . .TM transmit antennas. A receive signal x_(i) on an ith receiver antennais processed by a corresponding processor 610. Generally, the processor610 includes an implementation of one of several receiver designs toobtain an estimate c of the transmitted calibration symbols.

A summed channel estimates block 630 sums the transmission channelelements corresponding with each receiver antenna.

For a maximum likelihood receiver implementation;c ^(i) =argmin∥x _(i) −h ^(i) c∥ _(F), where ∥.∥ is the Frobenius norm,and h^(i) is a summed scalar channel. That is, h^(i) (the summed channelscalar) can be determined by summing transmission channel elementscorresponding with the receiver antenna.

For a MMSE or ZF receiver implementations;c ^(i) =h ^(i*)(h ^(i) h ^(i*))⁻¹ x _(i)

The common phase and amplitude error e_(j) between an ith receiverantenna and the transmitter is calculated by comparing the transmittedcalibration symbol c and the estimate of the received calibration symbolc^(i) with a compare block 620. More specifically,e _(i)=(c ^(i))/(c).

The calculated common phase and amplitude errors can be used to correctestimated data symbols that are transmitted from the transmit antennasT1, T2 . . . TM, and received by the receiver antennas R1, R2 . . . RN.

FIG. 7 shows another embodiment of the invention. This embodiment isgenerally applicable to multiple transmitter antenna, multiple receiverantenna systems in which both the multiple transmitter chains and themultiple receiver chains are independent. Generally, independenttransmitter/receiver chains are synchronized to independent referenceoscillators, have different RF components, or each transmitter/receiverchain is geographical located in a different place.

This embodiment includes multiple transmit antennas T1, T2 . . . TM.Each transmit antenna transmits a corresponding calibration symbol c1,c2 . . . cM. The transmitted calibration symbols symbol c1, c2 . . . cMtravel through a transmission channel represented by a channel matrix H,and are received by receiver antennas R1, R2 . . . RN.

The H matrix includes M by N elements, in which each element can benumbered as indicated in FIG. 7.

A known transmission calibration symbols c_(j) is transmitted from a jthtransmit antennas. Zeroed or nulled symbols are transmitted from all theother transmit antennas. A receive signal x_(i) on an ith receiverantenna is processed by a corresponding processor 710. Generally, theprocessor 710 includes an implementation of one of several receiverdesigns to obtain an estimate c of the transmitted calibration symbols.The estimate is of a calibration symbol transmitted from the jthtransmission antenna and received by the ith receiver antenna and isdesignated by c_(j) ^(i).

A channel element selector 720 selects each element within the channelmatrix H corresponding with the non-zeroed transmit antenna and thepresent receive antenna.

For an ML receiver, an estimate of c_(j) ^(i) can be given as:c _(j) ^(i) =argmin∥x _(i) −h _(ij) c _(j)∥_(F).

For an MMSE or ZF receiver, an estimate of c_(j) ^(i) can be given as:c _(j) ^(i)=(h _(ij))⁻¹ x _(i)

The common phase and amplitude error e_(j) between an ith receiverantenna and the jth transmitter antenna is calculated by comparing thetransmitted calibration symbol c and the estimate of the receivedcalibration symbol c^(i) with a compare block 730. More specifically,e _(ij)=(c _(j) ^(i))/(c _(j)).

The calculated common phase and amplitude errors can be used to correctestimated data symbols that are transmitted from the transmit antennasT1, T2 . . . TM, and received by the receiver antennas R1, R2 . . . RN.A correction block 740 provides correction of the elements within thechannel matrix H based upon the common phase and amplitude errors.

FIG. 8 shows another embodiment of the invention. This embodiment isgenerally applicable to multiple transmitter antenna, multiple receiverantenna systems in which both the multiple transmitter chains and themultiple receiver chains are independent. Generally, independenttransmitter/receiver chains are synchronized to independent referenceoscillators, have different RF components, or each transmitter/receiverchain is geographical located in a different place.

This embodiment includes multiple transmit antennas T1, T2 . . . TM.Each transmit antenna transmits a corresponding calibration symbol c1,c2 . . . cM. The transmitted calibration symbols symbol c1, c2 . . . cMtravel through a transmission channel represented by a channel matrix H,and are received by receiver antennas R1, R2 . . . RN.

The H matrix includes M by N elements, in which each element can benumbered as indicated in FIG. 8.

This embodiment is adaptable for use within wireless transmissionsystems that utilize multiple carrier transmission (like the previouslymention OFDM transmission), or transmit during predefined time slots.

OFDM systems include multiple carriers (or tones) that dividetransmitted data across the available frequency spectrum. In OFDMsystems, each tone is considered to be orthogonal (independent orunrelated) to the adjacent tones. OFDM systems use bursts of data, eachburst of a duration of time that is much greater than the delay spreadto minimize the effect of ISI caused by delay spread. Data istransmitted in bursts, and each burst consists of a cyclic prefixfollowed by data symbols, and/or data symbols followed by a cyclicsuffix.

As shown in FIG. 8, known transmission calibration vectors c(t1)= . . .=c(tT) are transmitted during multiple time slots or on multiplecarriers. The other time slots or carriers are nulled. The number oftransmit antennas and the number of tones/time slots can vary. A firstchannel matrix H(t1) corresponds with a first time slot/first carrier,and a second channel matrix h(t2) corresponds to with a second timeslot/second carrier.

Received signals at tones/slots t1 . . . tT can be represented as x(t1),. . . x(tT). The received signals can be processed by a processor 810.The receiver processing can be implemented as a ML receiver as follows:c ^(i) =argmin _(c) ∥x−cH∥ _(F), in which${x = \begin{bmatrix}{x_{i}\left( t_{1} \right)} \\\vdots \\{x_{i}\left( t_{T} \right)}\end{bmatrix}},$and ${H = \begin{bmatrix}{h_{i}\left( t_{1} \right)} \\\vdots \\{h_{i}\left( t_{T} \right)}\end{bmatrix}},$and where

-   -   ∥.∥_(F) is the Frobenius norm.

The receiver processing can also be implemented as an MMSE receiver asfollows:c ^(i) =H*(HH*+R _(nn))⁻¹ x ₁, where R_(nn) is a noise covariance matrixestimated at the receiver across the tones/slots t1 . . . tT and thereceiver antennas 1 . . . RN.

The common phase and amplitude error e_(j) between an ith receiverantenna and the jth transmitter antenna is calculated by comparing thetransmitted calibration symbol c and the estimate of the receivedcalibration symbol c^(i) with a compare block 820. More specifically,e _(ij)=(c _(j) ^(i))/(c _(i)).

The calculated common phase and amplitude errors can be used to correctestimated data symbols that are transmitted from the transmit antennasT1, T2 . . . TM, and received by the receiver antennas R1, R2 . . . RN.A correction block 830 provides correction of the elements within thechannel matrices H(t1), H(t2) based upon the common phase and amplitudeerrors.

FIG. 9 shows a flow chart of steps or acts included within an embodimentof the invention. This embodiment includes method of estimating commonamplitude and phase errors of a multiple channel wireless system. Themultiple channel wireless system includes a plurality of transmissionchannels formed between a plurality of transmission antennas and aplurality of receiver antennas.

A first step 910 includes estimating transmission channel elementsbetween each transmission antenna and receiver antenna pair of themultiple channel wireless system.

A second step 920 includes transmitting calibration symbols from eachtransmit antenna.

A third step 930 includes receiving signals corresponding to thecalibration symbols having traveled through the transmission channels.

A fourth step 940 includes estimating received calibration symbols basedupon spatial processing of the received signals and the estimatedtransmission channel elements.

A fifth step 950 includes estimating common amplitude and phase errorsfor each transmit and receive antenna pair by comparing the transmittedcalibration symbols with the received calibration symbols.

FIG. 10 shows a flow chart of steps or acts included within anembodiment of the invention. This embodiment includes a method ofestimating common amplitude and phase errors of a multiple channelwireless system. The multiple channel wireless system includes aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna.

A first step 1010 includes estimating transmission channel elementsbetween each transmission antenna and receiver antenna pair of themultiple channel wireless system for a plurality of carriers of amultiple carrier transmission signal.

A second step 1020 includes transmitting calibration symbols from eachtransmit antenna for the plurality of carriers of the multiple carriertransmission signal.

A third step 1030 includes receiving signals corresponding to thecalibration symbols having traveled through the transmission channels.

A fourth step 1040 includes estimating received calibration symbolsbased upon spatial processing of the received signals and the estimatedtransmission channel elements.

A fifth step 1050 includes estimating common amplitude and phase errorsfor each transmit and receive antenna pair by comparing the transmittedcalibration symbols with the received calibration symbols.

FIG. 11 shows a flow chart of steps or acts included within anembodiment of the invention. This embodiment includes a method ofestimating common amplitude and phase errors of a multiple channelwireless system. The multiple channel wireless system includes aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna.

A first step 1110 includes estimating transmission channel elementsbetween each transmission antenna and receiver antenna pair of themultiple channel wireless system for a plurality of transmission timeslots.

A second step 1120 includes transmitting calibration symbols from eachtransmit antenna for the plurality of transmission time slots.

A third step 1130 includes receiving signals corresponding to thecalibration symbols having traveled through the transmission channels.

A fourth step 1140 includes estimating received calibration symbolsbased upon spatial processing of the received signals and the estimatedtransmission channel elements.

A fifth step 1150 includes estimating common amplitude and phase errorsfor each transmit and receive antenna pair by comparing the transmittedcalibration symbols of the with the received calibration symbols.

FIG. 12 shows a flow chart of steps or acts included within anembodiment of the invention. This embodiment includes a method ofestimating common amplitude and phase errors of a multiple channelwireless system. The multiple channel wireless system includes aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna.

A first step 1210 includes estimating transmission channel elementsbetween each transmission antenna and receiver antenna pair of themultiple channel wireless system for a plurality of carriers of amultiple carrier transmission signal and a plurality of time slots.

A second step 1220 includes transmitting calibration symbols from eachtransmit antenna for the plurality of carriers of the multiple carriertransmission signal and plurality of time slots.

A third step 1230 includes receiving signals corresponding to thecalibration symbols having traveled through the transmission channels.

A fourth step 1240 includes estimating received calibration symbolsbased upon spatial processing of the received signals and the estimatedtransmission channel elements.

A fifth step 1250 includes estimating common amplitude and phase errorsfor each transmit and receive antenna pair by comparing the transmittedcalibration symbols of the with the received calibration symbols.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The invention islimited only by the claims.

1. A method of estimating common amplitude and phase errors of amultiple channel wireless system, the multiple channel wireless systemcomprising a plurality of transmission channels formed between aplurality of transmission antennas and a plurality of receiver antennas,the method comprising: estimating transmission channel elements betweeneach transmission antenna and receiver antenna pair of the multiplechannel wireless system; transmitting calibration symbols from eachtransmit antenna; receiving signals corresponding to the calibrationsymbols having traveled through the transmission channels; estimatingreceived calibration symbols based upon spatial processing of thereceived signals and the estimated transmission channel elements; andestimating common amplitude and phase errors for each transmit andreceive antenna pair by comparing the transmitted calibration symbolswith the received calibration symbols.
 2. The method of estimatingcommon amplitude and phase errors of a multiple channel wireless systemof claim 1, further comprising: correcting spatially processed receiveddata symbols with the estimated common amplitude and phase errors. 3.The method of estimating common amplitude and phase errors of a multiplechannel wireless system of claim 1, further comprising: correcting theestimated transmission channel elements with the estimated commonamplitude and phase errors.
 4. The method of estimating common amplitudeand phase errors of a multiple channel wireless system of claim 1,wherein transmission chains associated with the transmission antennasare independent, and receiver chains associated with the receiverantennas are dependent, the method further comprising: forming a channelmatrix from the transmission channel elements between each transmitantenna and receive antenna pair; and wherein the spatial processingcomprises: estimating the received calibration symbols using the channelmatrix and an equivalent maximum likelihood (ML) receiver structure. 5.The method of estimating common amplitude and phase errors of a multiplechannel wireless system of claim 1, wherein transmission chainsassociated with the transmission antennas are independent, and receiverchains associated with the receiver antennas are dependent, the methodfurther comprising: forming a channel matrix from the transmissionmultiplier estimates between each transmit antenna and receive antennapair; and wherein the spatial processing comprises: estimating thereceived calibration symbols using the channel matrix and an equivalentminimum mean squared error (MMSE) receiver structure.
 6. The method ofestimating common amplitude and phase errors of a multiple channelwireless system of claim 1, wherein transmission chains associated withthe transmission antennas are independent, and receiver chainsassociated with the receiver antennas are dependent, the method furthercomprising: forming a channel matrix from the transmission multiplierestimates between each transmit antenna and receive antenna pair; andwherein the spatial processing comprises: estimating the receivedcalibration symbols using the channel matrix and an equivalent zeroforcing (ZF) receiver structure.
 7. The method of estimating commonamplitude and phase errors of a multiple channel wireless system ofclaim 1, wherein transmission chains associated with the transmissionantennas are independent, and receiver chains associated with thereceiver antennas are dependent, the method further comprising: forminga channel matrix from the transmission multiplier estimates between eachtransmit antenna and receive antenna pair; and wherein the spatialprocessing comprises: estimating the received calibration symbols usingthe channel matrix and an equivalent decision feedback equalizer (DFE)receiver structure.
 8. The method of estimating common amplitude andphase errors of a multiple channel wireless system of claim 1, whereintransmission chains associated with the transmission antennas aredependent, and receiver chains associated with the receiver antennas areindependent, and wherein identical transmission calibration symbols aretransmitted from all of the transmission antennas; the method furthercomprising: generating a summed channel scalar for each receiver antennaby summing transmission channel elements corresponding with the receiverantenna; and wherein the spatial processing comprises: estimating thereceived calibration symbol for each receiver antenna using thecorresponding summed channel scalar and an equivalent maximum likelihood(ML) receiver structure.
 9. The method of estimating common amplitudeand phase errors of a multiple channel wireless system of claim 1,wherein transmission chains associated with the transmission antennasare dependent, and receiver chains associated with the receiver antennasare independent, and wherein identical transmission calibration symbolsare transmitted from all of the transmission antennas; the methodfurther comprising: generating a summed channel scalar for each receiverantenna by summing transmission channel elements corresponding with thereceiver antenna; and wherein the spatial processing comprises:estimating the received calibration symbol for each receiver antennausing the corresponding summed channel scalar and a zero forcing (ZF)receiver structure.
 10. The method of estimating common amplitude andphase errors of a multiple channel wireless system of claim 1, whereintransmission chains associated with the transmission antennas areindependent, and receiver chains associated with the receiver antennasare independent, and wherein transmitting calibration symbols from eachtransmit antenna comprises progressively transmitting calibrationsymbols from each transmission antenna while all other transmissionantennas are zeroed; and further comprising: forming an inverted channelelement by inverting the transmission channel elements for each transmitantenna and receive antenna pair; and estimating the receivedcalibration symbol for each receiver antenna based upon spatialprocessing of the received signals of the corresponding receiver antennaand the corresponding inverted channel element.
 11. A method ofestimating common amplitude and phase errors of a multiple channelwireless system, the multiple channel wireless system comprising aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna, the methodcomprising: estimating transmission channel elements between eachtransmission antenna and receiver antenna pair of the multiple channelwireless system for a plurality of carriers of a multiple carriertransmission signal; transmitting calibration symbols from each transmitantenna for the plurality of carriers of the multiple carriertransmission signal; receiving signals corresponding to the calibrationsymbols having traveled through the transmission channels; estimatingreceived calibration symbols based upon spatial processing of thereceived signals and the estimated transmission channel elements; andestimating common amplitude and phase errors for each transmit andreceive antenna pair by comparing the transmitted calibration symbolswith the received calibration symbols.
 12. The method of estimatingcommon amplitude and phase errors of a multiple channel wireless systemof claim 11, wherein the spatial processing comprises: estimatingreceived calibration symbols using the estimated transmission channelelements and an equivalent of at least one of an ML, MMSE, ZF and DFEreceiver structures.
 13. A method of estimating common amplitude andphase errors of a multiple channel wireless system, the multiple channelwireless system comprising a plurality of transmission channels formedbetween at least one transmission antenna and at least one receiverantenna, the method comprising: estimating transmission channel elementsbetween each transmission antenna and receiver antenna pair of themultiple channel wireless system for a plurality of transmission timeslots; transmitting calibration symbols from each transmit antenna forthe plurality of transmission time slots; receiving signalscorresponding to the calibration symbols having traveled through thetransmission channels; estimating received calibration symbols basedupon spatial processing of the received signals and the estimatedtransmission channel elements; and estimating common amplitude and phaseerrors for each transmit and receive antenna pair by comparing thetransmitted calibration symbols of the with the received calibrationsymbols.
 14. The method of estimating common amplitude and phase errorsof a multiple channel wireless system of claim 13, wherein the spatialprocessing comprises: estimating received calibration symbols using theestimated transmission channel elements and an equivalent of at leastone of an ML, MMSE, ZF and DFE receiver structures.
 15. A method ofestimating common amplitude and phase errors of a multiple channelwireless system, the multiple channel wireless system comprising aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna, the methodcomprising: estimating transmission channel elements between eachtransmission antenna and receiver antenna pair of the multiple channelwireless system for a plurality of carriers of a multiple carriertransmission signal and a plurality of time slots; transmittingcalibration symbols from each transmit antenna for the plurality ofcarriers of the multiple carrier transmission signal and plurality oftime slots; receiving signals corresponding to the calibration symbolshaving traveled through transmission channels; estimating receivedcalibration symbols based upon spatial processing of the receivedsignals and the estimated transmission channel elements; and estimatingcommon amplitude and phase errors for each transmit and receive antennapair by comparing the transmitted calibration symbols of the with thereceived calibration symbols.
 16. The method of estimating commonamplitude and phase errors of a multiple channel wireless system ofclaim 15, wherein the spatial processing comprises: estimating receivedcalibration symbols using the estimated transmission channel elementsand an equivalent of at least one of an ML, MMSE, ZF and DFE receiverstructures.
 17. An apparatus for estimating common amplitude and phaseerrors of a multiple channel wireless system, the multiple channelwireless system comprising a plurality of transmission channels formedbetween a plurality of transmission antennas and a plurality of receiverantennas, the apparatus comprising: means for estimating transmissionchannel elements between each transmission antenna and receiver antennapair of the multiple channel wireless system; means for transmittingcalibration symbols from each transmit antenna; means for receivingsignals corresponding to the calibration symbols having traveled throughthe transmission channels; means for estimating received calibrationsymbols based upon spatial processing of the received signals and theestimated transmission channel elements; and means for estimating commonamplitude and phase errors for each transmit and receive antenna pair bycomparing the transmitted calibration symbols with the receivedcalibration symbols.
 18. An apparatus for estimating common amplitudeand phase errors of a multiple channel wireless system, the multiplechannel wireless system comprising a plurality of transmission channelsformed between at least one transmission antenna and at least onereceiver antenna, the apparatus comprising: means for estimatingtransmission channel elements between each transmission antenna andreceiver antenna pair of the multiple channel wireless system for aplurality of carriers of a multiple carrier transmission signal; meansfor transmitting calibration symbols from each transmit antenna for theplurality of carriers of the multiple carrier transmission signal; meansfor receiving signals corresponding to the calibration symbols havingtraveled through the transmission channels; means for estimatingreceived calibration symbols based upon spatial processing of thereceived signals and the estimated transmission channel elements; andmeans for estimating common amplitude and phase errors for each transmitand receive antenna pair by comparing the transmitted calibrationsymbols with the received calibration symbols.
 19. An apparatus forestimating common amplitude and phase errors of a multiple channelwireless system, the multiple channel wireless system comprising aplurality of transmission channels formed between at least onetransmission antenna and at least one receiver antenna, the apparatuscomprising: means for estimating transmission channel elements betweeneach transmission antenna and receiver antenna pair of the multiplechannel wireless system for a plurality of transmission time slots;means for transmitting calibration symbols from each transmit antennafor the plurality of transmission time slots; means for receivingsignals corresponding to the calibration symbols having traveled throughthe transmission channels; means for estimating received calibrationsymbols based upon spatial processing of the received signals and theestimated transmission channel elements; and means for estimating commonamplitude and phase errors for each transmit and receive antenna pair bycomparing the transmitted calibration symbols of the with the receivedcalibration symbols.
 20. An apparatus for estimating common amplitudeand phase errors of a multiple channel wireless system, the multiplechannel wireless system comprising a plurality of transmission channelsformed between at least one transmission antenna and at least onereceiver antenna, the apparatus comprising: means for estimatingtransmission channel elements between each transmission antenna andreceiver antenna pair of the multiple channel wireless system for aplurality of carriers of a multiple carrier transmission signal and aplurality of time slots; means for transmitting calibration symbols fromeach transmit antenna for the plurality of carriers of the multiplecarrier transmission signal and plurality of time slots; means forreceiving signals corresponding to the calibration symbols havingtraveled through the transmission channels; means for estimatingreceived calibration symbols based upon spatial processing of thereceived signals and the estimated transmission channel elements; andmeans for estimating common amplitude and phase errors for each transmitand receive antenna pair by comparing the transmitted calibrationsymbols of the with the received calibration symbols.